Method of making an optically readable element

ABSTRACT

According to a first aspect of the present invention, there is provided a method of making an optically readable element, the method comprising: providing one or more optically readable structures in or on a body, a strain being applied to the one or more optically readable structures as a result of an interaction between the body and the one or more optically readable structures; the one or more optically readable structures each having an intrinsic band structure prior to application of the strain, and wherein the applied strain changes that intrinsic band structure; and wherein the interaction is such that the strain is maintained, after the element has been made, without the need for an external influence.

The present invention relates generally to a method of making anoptically readable element, and to a system for making an opticallyreadable element, and to a related optically readable element, forexample one made using the method or system.

An optically readable element can take one of a range of differentforms. Such an element may be read by an electronic sensor or similar,or by the eye of a human user. In one example, an optically readableelement might be or form part of a display device, or general visualdisplay. In another example, an optically readable element may be usedfor different purposes, or for simultaneous purposes, for example foruse in providing or otherwise determining a unique identifier. Forinstance, an optically readable element might take the form of abarcode, QR code, a hologram, a smart ink, or other form of identifier,or similar. The optically readable element might be, take the form of,or otherwise provide a physically (or physical) unclonable function(PUF).

Many years ago, optically readable elements may have been rathersimplistic or even classical in form, for example comprising a paintedsurface, a lightbulb behind a coloured filter or similar, all the waythrough to a rather basic black and white line barcode, or related QRcode. However, in more recent years, optically readable elements havebecome more advanced and more sophisticated, for example relying onsemiconductor structures, structures exhibiting quantum mechanicalconfinement, and generally structures that have an intrinsic bandstructure that is directly related to the optical properties of thestructure. Existing methods and systems for making such opticallyreadable elements comprising such band structures might be suitable incertain circumstances, performing and creating optically readableelements as intended for the application in question.

However, while the intrinsic band structures of such optical structuresmay give advantageous properties in some examples, for example in termsof electromagnetic radiation emission profiles or energy efficiencies,those same band structures may provide disadvantageous features, forexample undesirable or unintended electromagnetic radiation emissionprofiles. It may therefore be desirable to ensure that such emissionprofiles are in some way controlled or controllable to realise adesirable emission profile. Perhaps counterintuitively, the somewhatopposite situation might also arise, where it may be desired to ensurethat an emission profile is altered or otherwise changed for use inestablishing or improving a unique identity provided by the relatedoptical structures, for example establishing or increasing the‘uniqueness’ of a physically unclonable function provided by thosestructures.

It is an aim of example embodiments of the present invention to at leastpartially avoid, solve or overcome one or more disadvantages of theprior art, whether identified herein or elsewhere, or to at leastprovide an alternative to existing approaches in the prior art.

According to example embodiments of the present invention, there isprovided a method of making an optically readable element, a system formaking an optically readable element, and optically readable element,all as defined in the independent claims. Additional features will beapparent from the dependent claims, and the present disclosure as awhole.

According to a first aspect of the present invention, there is provideda method of making an optically readable element, the method comprising:providing one or more optically readable structures in or on a body, astrain being applied to the one or more optically readable structures asa result of an interaction between the body and the one or moreoptically readable structures; the one or more optically readablestructures each having an intrinsic band structure prior to applicationof the strain, and wherein the applied strain changes that intrinsicband structure; and wherein the interaction is such that the strain ismaintained, after the element has been made, without the need for anexternal influence.

The interaction may be based on a change in state of the body from afirst state to a second state.

The change in state is linked to one or more of, or a combination of: atleast partial solidification of the body; and/or thermal expansion orcontraction of the body; and/or curing of the body.

A second body may be provided, covering at least a part of the body inor on which the one or more optically readable structures have beenprovided.

The provision of the second body might also apply a strain to the one ormore optically readable structures as a result of a direct or indirectinteraction between the second body and the one or more opticallyreadable structures.

One or both of the body and the second body may provide one or more of,or a combination of: optical filtering with respect to optical readingof the one or more optically readable structures; and/or protection forthe one or more optically readable structures; and/or stabilisation ofan optical property of the one or more optically readable structures;and/or a degree of control of an average strain at an interface betweenthe body and the second body.

One or more optically readable structures may be provided in or on asupport. The providing one or more optically readable structures in oron the body may comprise locating the support on the body. Theinteraction may be directly between the body and the one or moreoptically readable structures, and/or the interaction may be indirectlybetween the body and the one or more optically readable structures viathe support.

The applied strain may be controlled, in terms of magnitude and/ordirection of the applied strain.

The applied strain may be uncontrolled, in that it is not possible to(e.g. easily) predict (e.g. without inspection or testing) a particularmagnitude and/or a particular direction of the applied strain on one,more or all of the one or more optically readable structures.

The one or more optically readable structures may be or comprise one ormore continuous (e.g. a layer, optionally comprising defects) ordiscrete components (e.g. dots, particles, flakes) exhibiting quantummechanical confinement, the or each component having an intrinsic bandstructure prior to application of the strain, and wherein the appliedstrain changes that intrinsic band structure. The change in bandstructure is in order to change an optical property of the componentlinked to that quantum mechanical confinement. The confinement of theone or more continuous or discrete components optionally confines in oneor more of 3D, 2D, or 1D, or 0D.

The one or more optically readable structures may comprise a 2Dmaterial, or may confine in 2D, or may comprise 0D quantum dots or mayconfine in 0D. The strain may optionally be axially applied to the body,e.g. such that the material is strained along/parallel to its length orwidth, and not across its depth.

The interaction may be such that the strain is maintained, after theelement has been made, without the need for an external influence in theform of one or more of: an externally applied temperature change; anexternally applied force. That is, without external influence, theapplied strain is maintained.

According to a second aspect of the present invention, there is provideda system for making an optically readable element, the systemcomprising: a dispenser for providing one or more optically readablestructures in or on a body, a strain being applied to the one or moreoptically readable structures as a result of an interaction between thebody and the one or more optically readable structures; the one or moreoptically readable structures each having an intrinsic band structureprior to application of the strain, and wherein the applied strainchanges that intrinsic band structure; and wherein the interaction issuch that the strain is maintained without the need for externalinfluences, after the element has been made.

The system may also comprise an optical reader for optically reading theone or more optically readable structures of the optically readableelement, e.g. as or just after the strain has been applied.

According to a third aspect of the present invention, there is providedan optically readable element comprising: one or more optically readablestructures in or on a body, a strain being applied to the one or moreoptically readable structures as a result of an interaction between thebody and the one or more optically readable structures; the one or moreoptically readable structures each having an intrinsic band structureprior to application of the strain, and wherein the applied strainchanges that intrinsic band structure; and wherein the interaction issuch that the strain is maintained without the need for externalinfluences, after the element has been made.

It will be apparent to the skilled person, after reading thisdisclosure, that one or more features described in relation to any oneor more aspect of the present invention may be used in combination with,or in place of, any one or more features of the another aspect of thepresent invention, unless such combination or replacement would beunderstood by the skilled person as mutually exclusive. In particular,it is to be made clear that any features described or defined inrelation to one or more of the method, system or element aspects may beinterchanged with or used in combination with any one or more of themethod, system and element aspects.

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made, byway of example, to the accompanying diagrammatic Figures in which:

FIG. 1 schematically depicts an optically readable element, and relatedprinciples of use;

FIG. 2 schematically depicts a graph of an emission profile of anoptically readable structure of the element of FIG. 1;

FIG. 3 schematically depicts a change in the emission profile of FIG. 2,with applied strain;

FIG. 4 schematically depicts a graph showing a change in the emissionprofile of FIG. 3, with further applied strain;

FIG. 5 schematically depicts methodology associated with a method ofmaking an optically readable element according to an example embodiment;

FIG. 6 schematically depicts methodology associated with a method ofmaking an optically readable element according to another exampleembodiment;

FIG. 7 schematically depicts methodology associated with a method ofmaking an optically readable element according to another exampleembodiment;

FIG. 8 schematically depicts a system for making an optically readableelement, in accordance with an example embodiment;

FIG. 9 is a flow chart schematically depicting general methodology formaking an optically readable element, according to an exampleembodiment;

FIG. 10 schematically depicts general principles of a system for makingan optically readable element, according to an example embodiment; and

FIG. 11 schematically depicts general principles associated with anoptically readable element, according to example embodiments.

It is known that applying a strain to an optically readable structurehaving an intrinsic band structure can be used to alter that intrinsicband structure, in order to alter optical properties of that opticallyreadable structure. This includes the structure being opticallyreadable, or more easily optically readable, or readable in a certainmanner, only when or after strain has been applied. That is, theapplication of strain ensures that the structure (e.g. a semiconductorstructure or more generally a structure having an intrinsic bandstructure) becomes optically readable in a certain manner—e.g. frombeing optically readable to note that it does not emit, to opticallyreadable to note that it does emit. For the purposes of this disclosure,and for simplicity, this is still generally to be understood as anoptically readable structure.

Altering the band structure might be defined or described as altering orchanging a profile of a conduction band, or a profile of a valence band,or a profile between such bands, or any alteration of the structure ingeneral. In existing approaches, changing of such properties has beenundertaken in a laboratory or experimental fashion, for example using anexternal (to the structure or element) heating stage that carefullycontrols a temperature or temperature change applied to the opticallyreadable structures, or by carefully controlling an external force thatis applied to the structures, or element in general. However, accordingto example embodiments of the present invention, it has been realisedthat changes or alterations in the intrinsic band structure can bein-built, such that the changes are maintained after the opticallyreadable element has been made, which is not the case for the approachesdiscussed previously. In other words, the changes or alterations in theintrinsic band structure can be in-built, and do not require externalinfluences (e.g. externally originating temperature changes or forces)to achieve. This means that no external power is required to maintainthe strain. For example, if the element is attached to an object, thestrain remains, either intrinsically or via interaction with thatobject, yet no external heating stage or powered actuator is required.

According to the present invention, there is generally provided a methodof making an optically readable element. The method comprises providingone or more optically readable structures in or on a body. A strain isapplied to the one or more optically readable structures as a result ofan interaction between the body and the one or more optically readablestructures. That is, an external influence is not required. The one ormore optically readable structures each have an intrinsic band structureprior to the application of the strain. The applied strain changes thatintrinsic band structure, and thus one or more optical properties of theoptically readable structure or structures.

The interaction is such at the strain is maintained after the elementhas been made, without the need for an external influence (e.g.externally applied temperature change or externally applied force). Thismeans that the change in optical property can be maintained andpermanently realised, for example in use of, or otherwise generalinteraction with, the optically readable element.

The changes in the intrinsic band structure across one or more opticalreadable elements may be undertaken in one example to improve opticaloutput or performance, for example improving uniformity of opticaloutput across one or more optically readable structures, or in some waytuning the output to a desired output (e.g. wavelength or similar).Conversely, the changes that are in-built may be such that a random ornondeterministic strain is applied, to ensure that a random ornondeterministic change in band structures is realised, which can forexample be used to create or strengthen a unique identifier associatedwith the optically readable structure or structures (e.g. one or morereadable optical properties of any one or more optical structures acrossthe optically readable element).

The Figures will now be used to describe features of, or relating to,the present invention. The Figures are not drawn to any particularscale.

FIG. 1 schematically depicts a plan view of an optically readableelement 2. The optically readable element 2 comprises a number (e.g. oneor more, but in this example more than one) optically readablestructures 4. The optically readable structures 4 each have an intrinsicband structure which dictates the optical properties of the opticallyreadable structure 4. For example, changes to the intrinsic bandstructure might alter an emission strength and/or wavelength of thestructure 4, as well as absorption properties. This will, of course,impact how electromagnetic radiation is emitted (which includesreflecting or scattering) from the structures 4.

In the example of FIG. 1, the optically readable structures 4 compriseor take the form of flakes of a two-dimensional (2D) material. However,and more generally, the one or more optically readable structures 4could comprise one or more continuous (e.g. a layer, optionallycomprising defects) or discrete (e.g. dots, particles, flakes)components exhibiting quantum mechanical confinement. Typically, suchstructures will have the intrinsic band structure discussed herein, butwill also have particularly useful properties in terms of particularemission or absorption wavelengths, or sharp transitions, energyefficiencies, etc. The confinement might typically be in one or more of3D, 2D, 1D or 0D. As discussed herein, strain may be used to change theband structure of such materials, and thus the optical properties ofsuch materials. 2D materials or those materials exhibiting 2Dconfinement (e.g. flakes or layers), or 0D materials or materialsexhibiting 0D confinement (e.g. quantum dots), are known to beparticularly susceptible to the application of strain, and so might findparticular use in the application of the present invention. This isparticularly true when the strain is applied axially with regard to thestructure in question.

A 2D material might be defined or described as a material that isatomically thin in one dimension only, e.g. not necessary a single layerof a few atoms thick, but thin enough that electrons behave quantummechanically, for example being confined and/or such that motion ofelectrons into, and out of, a two dimensional plane of the material isgoverned by quantum mechanical effects. The minimumwidth/depth/dimension is material-dependent.

FIG. 1 shows the optically readable element 2 being irradiated withexcitation electromagnetic radiation 6. The excitation 6 causes theoptically readable structures 4 to emit 8 emission radiation, forexample by (e.g. non-resonant) photoluminescence. FIG. 2 shows asimplified representation of an emission spectrum 10 (or profile) for anoptically readable structure 4, or for part of such a structure 4. Theemission spectrum 10 is shown on a graph of emission wavelength 12versus emission intensity 14. For this particular explanation, the exactnumerical details are not of significant consequence for explainingunderlining principles relating to the present invention.

FIG. 3 is another graph, this time showing the change in an emissionprofile 20 (compared with that in FIG. 2) as a result of strain 22 beingapplied to the optically readable structure exhibiting that profile. Thestrain is in-built, in that it is intrinsically locked-in to theelement, such that the strain is applied without the need for externalinfluences.

Again, while the numerical or otherwise quantitative details of thechange emission profile are largely irrelevant for a generalappreciation of the principles underlying the present invention, it canbe seen that the application of strain 22 has changed the intrinsic bandstructure of the optically readable structure, which has in turn had animpact on its emission profile 20.

It will appreciated that this strain 22, can be used to ensure that theresulting emission profile 20 is a desired emission profile 20, forexample one having a particular emission wavelength or similar. Thisapproach might therefore be used to tune the optical properties of thosestructures, for example selectively across one or more areas of theoptically readable element comprising one or more optically readablestructures. In a crude example, the emission may be made to be bluer, orredder, or generally a different colour, and so on.

FIG. 4 is, again, a graph similar in form to those already shown in andwith described reference to FIGS. 2 and 3 above. However, thisparticular graph shows how the emission profile 20 shown in FIG. 3 may,itself, be changed with the application of further strain 30 to a new,and different, emission profile 32. This change or further change inprofile 32 due to the strain changing 30 could be used, for example, tofurther change the profile so that it is a desired emission profile 32.Again, this change could be a deliberate locked-in change as part ofmanufacturing of the element.

However, in some examples, perhaps the opposite is true. For example, ifthe change in strain 30 (or simple strain in general) is not known, forexample in terms of its magnitude or its direction or similar, then thechange in emission profile 32 may also not be known in advance. In otherwords, an unknown or random (e.g. change in) strain 30 should result inan unknown or a random change in the emission profile 32. This effectcan be used to introduce or strengthen a unique identifier provided bythe one or more emission profiles of the one or more optically readablestructures of the optical element, or to strengthen this uniqueidentifier. For instance, if the one or emission profiles (or dataindicative thereof) were mapped for one or more emission locationsacross the optically readable element (e.g. for one or more opticallyreadable structures), then this might be used to provide a uniqueidentifier or fingerprint for the optically readable element, whichcould be used in providing authentication or proving authenticity of theoptically readable element, or a device or other object to which theelement is attached. In this scenario, the effect of introducing someform of random or non-deterministic strain across the element, andtherefore to the one or more optically readable structures, could beviewed in a number of different ways.

For one example, even if it is somehow possible (although of courseextremely unlikely) to replicate the location of the one or moreoptically readable structures, and their physical composition, to insome way mimic or fool an authentication system or element (in otherwords, to try clone the optical element), it would be even harder to tryand replicate some form of in-built and randomly introduced strain. Thestrain, or strain field, adds an extra dimension of security to theelement, making it harder to copy. The physical properties of quantummaterials (e.g. those having intrinsic band structures, and optionallyexhibiting confinement) are much more sensitive to strain than classicalmaterials. In this way the optical changes induced by the random strainfield also act to highlight the actual presence of quantum materials, asopposed to a material (e.g. counterfeit or otherwise) pretending to besuch a material—i.e. the introduction of strain is in some ways a checkfor the presence of quantum materials (e.g. those having intrinsic bandstructures, and optionally exhibiting confinement).

From another perspective, if an optically readable element already had astrain-field built into its structure by interaction between a body ofmaterial and the optically readable structures in or on that body, thenthe optical properties of the one or more optically readable structuresacross the optical element will have unique emission profiles, leadingto a fingerprint or a unique identifier for the optically readableelement. The same is true, even if the strain-field is zero. If,however, the strain-field is then changed, this means that the opticalproperties of the optical readable structures will also change. Thiswill, of course, change the fingerprint or unique identifier provided bythe optical element. The reasons why this might be useful might, infact, be counterintuitive. One reason is that if the optical element istampered with, for example delaminated or removed from a product, orotherwise bent or deformed and so on, this will impact thatstrain-field. So, whereas the optical element might pass someauthentication test or process in one instance, it may not pass asecond, subsequent authentication process or test at a second instance,after such tampering has taken place, as a result of changes in thestrain-field and consequent changes in the identifier or fingerprintprovided by the changes in the optical structure of the element. So, insummary, in this particular example, changes in the in-builtstrain-field may be used an anti-tampering mechanism or process. Theexact nature or changes of the strain or resulting optical properties donot necessarily need to be qualified or quantified, and all that needsto happen is for the degree of strain to be sufficient to change thefingerprint, signature or unique identifier of the device to somethingdifferent to that recognised or determined previously, so that anyauthentication process is no longer passed. Therefore, theanti-tampering mechanism is very simple to implement, yet extremely hardto avoid. This sort of anti-tampering is not possible with classicalmaterials.

When used in a security or authentication environment or application,the optically readable element might be defined or described as anoptically readable security element, an optically readable identifier,an optically readable PUF, and so on.

Various approaches may be used to establish an in-built strain orstrain-field within the optical element. Different examples will now bedescribed.

FIG. 5 schematically depicts a container 40, containing a solution ofpolymer and optically readable structures in the form of flakes of 2Dmaterial 42. The solution 42 is then provided on a substrate or othersupport 44.

Over time, and as part of the manufacturing process of an opticalelement using the solution 42 and substrate 44, the solution 42 willchange from a first state to a second state, which will result in astrain 46 being applied to optically readable structures in thatsolution. The change in state from the first state to the second statemay be any one or more of, or a combination of, at least partialsolidification of the body in which the optically readable structuresare located; thermal expansion or contraction of that body; or curing ofthe body. These changes might be changes directly associated with thebody, or indirectly via an interaction with the substrate 44 or othersupport.

In this example, the body may be one or more parts of the solution, orsimply a matrix or other material in which the optically readablestructures are present. Changes to the body will directly or indirectlyimpact the optically readable structures, such that if a strain-field isinduced within the body, strain will be applied, and maintained, to theoptically readable structures.

The final body-substrate 42, 44 combination may form the opticallyreadable element discussed above. The body might form a film or otherlayer on the substrate 44. The substrate 44 may not form a part of thefinal optically readable element. That is, the body 42 might be removed,once cured or similar.

The application or final ‘setting’ of the body may be undertaken insomething of a controlled manner, for example in terms of a direction ofapplication, or a condition during setting, such that the degree ofstrain is in someway controlled, for example in terms of direction ormagnitude. This might be helpful, for example, in ensuring or improvingsome form of uniformity in the applied strain, and the resulting changesin optical properties of the optically readable structures. In anotherexample, there may, very deliberately, be little or no considerationgiven to the degree of control of application or setting of the body,such that the results of the strain-field applied on or within the bodyand thus to optically structures, is random. Randomness can sometimesimprove overall or average uniformity, e.g. when the element is taken aswhole, or read from a great distance. However, randomness giveslocalised non-uniformity, giving or strengthen a unique identifier, asdiscussed above.

It will be noted that providing the one or more optically readablestructures within a body of material might, or in some examples should,result in the optically readable structures being distributed not onlyacross the body and optically readable element, but also within (thatis, with different depths in) the body of the optically readableelement. This might allow for an optical reading of the opticallyreadable element to have an angular dependence—i.e. the reading changeswith angle, due to a 3D distribution of optically readable structureswithin the optically readable element. This might add another dimensionto the security or uniqueness of the element, making it even harder tocopy. This is opposed to a purely 2D distribution, that might be easierto replicate.

Depending on the application in question, the body in or on which theoptically readable element is provided may be rigid or flexible. In someexamples, a rigid application might be desired such that the resultingstructure is either resistant to damage to give robustness, or is verysusceptible to damage making it harder to tamper with. Alternatively, aflexible configuration might be advantageous, so that the opticallyreadable can be flexed without damage and therefore be more robust, orso that the element can be flexed and returned to its originalconfiguration without a permanent change to its in-built strain-field,which could otherwise compromise future authentications of that element.

FIG. 6 shows how one or more optically readable structures have beenprovided in a support polymer matrix or body 50. For instance, theoverall structure might comprise a number of optically readablestructures embedded in a film or tape-like structure 50. The structure(support and optically readable structures) 50 may be applied to anotherbody 52 in the form of a substrate or similar. This application, or theresulting settling or establishing of some form of equilibriumrelationship, may result in there being a differential relationshipbetween the body 52 and the support 50. This might result in aninteraction which results in a strain being applied directly orindirectly to the structures with the support 50. Again, a strain-fieldis provided, impacting the optical properties of the optically readablestructures. Alternatively, there might already be a strain-field builtinto the structure 50 prior to application. Application might not changethis field. Application might change this field.

To some extent, the terms “support” and “body” may be usedinterchangeably. The point is that some form of interaction resultswhich changes or otherwise impacts the strain applied to the opticallyreadable elements. This could be treated in a number of different ways,as already discussed above, and further below. So, the strain could bein-built within the body in an intrinsic manner. Or, applying a supportto a body (or vice versa) might establish the required in-builtstrain-field. This means that no external power is required to maintainthe strain. For example, if the element is attached to an object, thestrain remains, either intrinsically or via interaction with thatobject, yet no external heating stage or powered actuator is required.

FIG. 7 schematically depicts a different optically readable element. Afirst body is provided, for example in the form of a first polymer layer60. On top of that polymer layer 60 is provided a layer of opticallyreadable structures, optionally within a polymer matrix or other body ofmaterial. Located on top of those optically readable structures 62 is asecond body 64, for example a second polymer layer 64.

Different degrees or extents of strain can be applied to the opticallyreadable structure 62 for a number of different reasons. Application ofthe optically readable structures to the first layer 60 may result in astrain-field being induced, for example as described in relation to FIG.5. Alternatively or additionally, the provision of the second layer 54on top of the optically readable structure 62 may have a similareffect—i.e. introduction of a strain-field to the optically readablestructures 62. Indeed, the strain-field introduced to the opticallyreadable structures will likely have a contribution from each of thelayers 60, 64, and to that extent the strain-field might at least bepartially controlled (for example at least an average strain or similar)by consideration or appropriate choice of the nature of the first layer60 and second layer 64 and or related processing conditions.

The presence of the second body 64 might, in particular, have advantagesin addition to or separate from any introduction or contribution to astrain-field. For instance, the second body 64 or layer might provideoptical filtering with respect to optical reading of the one or moreoptically readable structures 62. The second layer 64 might provideprotection for the one or more optically readable structures 62. Thesecond layer 64 might provide a degree of encapsulation (e.g.stabilisation) of an optical property of the one or more opticalreadable structure 62, for example, preventing the optical property fromdrifting or degrading overtime or at least a significant period of time.

Generally, the bodies or supports described herein have one or moreproperties or functions as described in relation to the second body ofFIG. 7. The bodies or supports described herein might be transparent, atleast to excitation or emission electromagnetic radiation used in thereading of the element or its structures.

FIG. 8 schematically depicts a system for making (which includesproviding) an optically readable element 72. The system 70 comprises adispenser 74, for providing one or more optically readable structures inor on a body, a strain being applied the one or more optically readablestructures as a result of interaction between the body and the one ormore optically readable structures. The structures and/or body may beprovided on a substrate or other support 76 which may, depending on thenature of application, be an article to which the optical element 72 isto be attached, or which may form part of the optical element, forexample a backing or support layer.

The manner in which the dispenser 74 dispenses the optically readablestructures (which may include a related body in or on which thestructures are provided) may depend on the particular application forthe optically readable element. For example, the optically readablestructures may be dispensed in a manner similar to that shown inrelation to FIG. 5, for example in solution or fluidic-matrix form.However, the dispenser 74 might dispense the material in a differentway, similar to that shown in FIG. 6, where a sheet or strip in the formof a role or tape is dispensed by the dispenser 74, for example as thedispenser 74 or system 70 is moved relative to and across the support orsubstrate 76.

Conveniently, the system might comprise an optical reader 78 which maybe employed to optically read the optically readable structures (or theoptically readable element in general) as the dispensing takes place.This means that the application and reading of the structures orelements in general can be taken very quickly and very efficiently bythe same system. While this may be convenient in general, this mightalso be important for anti-counterfeiting or similar. If the uniquefingerprint or identifier provided by the one or more optically readablestructures is read immediately upon application (or very shortlyafterwards) then any tampering at some later time will be easilyidentifiable or actionable, either by noting the change in signature, orunique identity, or fingerprint, or simply by way of any subsequentauthentication check of the optically readable element failing due tochanges in a strain-field caused by tampering of or with the opticallyreadable element.

The optical reading may be undertaken by the optical reader 78 inambient or generally environmental lighting conditions. However, thesystem 70 might comprise a dedicated excitation source 79 for use, forexample, in exciting the optical readable structures for appropriatereading by the reader 78.

FIG. 9 schematically depicts a flow chart which identifies generalprinciples underlying the inventive concept. The method might compriseproviding one or more optically readable structures in or on a body 80.A strain is applied to the one or more optically readable structures asa result of an interaction between the body and the one or moreoptically readable structures 82. The one or more optically readablestructures each have an intrinsic band structure prior to application ofthe strain. The applied strain changes that intrinsic band structure.The interaction is such that the strain is maintained, after the elementhas been made, without the need for an external influence 84 (e.g.externally applied heat on an externally applied force).

FIG. 10 schematically depicts similarly generic principles associatedwith a system for making an optically readable element according toexample embodiments. The system comprises a dispenser 90 for providingone or more optically readable structures in or on a body, such that astrain may be applied to the one or more optically readable structuresas a result of an interaction between the body and the one or moreoptically readable structures. The one or more optically readablestructures each have an intrinsic band structure prior to application ofthe strain. The applied strain changes that intrinsic structure. Theinteraction between the body and the one or more optically readablestructures is such that the strain is maintained without the need for anexternal influence, after the element has been made. As discussed morespecifically above, the system might more generically include some formoptical reader 92 for optically reading the optically readablestructures as, or after, e.g. relatively quickly after, the opticalreadable element has been made or applied to some other support, body,or other structure (that is, when the strain field that is to be reliedupon for authentication or other functionality has been established andmaintained).

The system might be arranged to, and/or include a part of component to,apply the optically readable element to a surface. This could be thedispenser, or could be something else or additional, for example for usein attached an element to a surface using an adhesive or other fixingbody or structure.

FIG. 11 schematically depicts general principles of an opticallyreadable element 100 in accordance with example embodiments. The element100 comprises one or more optically readable structures in or on a body104. A strain is applied to the one or more optically readablestructures 102 as a result of an interaction between the body 104 andthe one or more optically readable structures 102. The one or moreoptically readable structures 102 each have an intrinsic band structureprior to application of the strain. The applied strain changes thatintrinsic band structure, and thus the optical properties of theoptically readable structure. The interaction is such that the strain ismaintained without the need for external influences, after the element100 has been made. The structure 102 and body 104 may be located on asupport or other body 106 which may form part of the element 100, orwhich may be used in the formation of the optically readable element100. The body itself 104 may be formed from setting or curing of somefluidic substance or similar. Alternatively or additionally, the body104 might be described as a support or similar, and take the form of atape or reel or film previously provided and applied to the underlyingsupport structure or substrate 106.

Although a few preferred embodiments have been shown and described, itwill be appreciated by those skilled in the art that various changes andmodifications might be made without departing from the scope of theinvention, as defined in the appended claims.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. A method of making an optically readable element, the methodcomprising: providing one or more optically readable structures at leastin or on a body, a strain being applied to the one or more opticallyreadable structures as a result of an interaction between the body andthe one or more optically readable structures; the one or more opticallyreadable structures each having an intrinsic band structure prior toapplication of the strain, and wherein the applied strain changes theintrinsic band structure; and wherein the interaction is such that thestrain is maintained, after the element has been made, independently ofan external influence.
 2. The method of claim 1, wherein the interactionis based on a change in state of the body from a first state to a secondstate.
 3. The method of claim 2, wherein the change in state is linkedto at least one of: at least partial solidification of the body; and/orthermal expansion or contraction of the body; and/or curing of the body.4. The method of claim 1, wherein a second body is provided covering atleast a part of the body in or on which the one or more opticallyreadable structures have been provided.
 5. The method of claim 4,wherein the provision of the second body also applies a strain to theone or more optically readable structures as a result of a direct orindirect interaction between the second body and the one or moreoptically readable structures.
 6. The method of claim 4, wherein one orboth of the body and the second body provide at least one of: opticalfiltering with respect to optical reading of the one or more opticallyreadable structures; protection for the one or more optically readablestructures; stabilisation of an optical property of the one or moreoptically readable structures; and control of an average strain at aninterface between the body and the second body.
 7. The method of claim1, wherein one or more optically readable structures are provided in oron a support, and the providing one or more optically readablestructures in or on the body comprises locating the support on the body,the interaction being directly between the body and the one or moreoptically readable structures, and/or the interaction being indirectlybetween the body and the one or more optically readable structures viathe support.
 8. The method of claim 1, wherein further comprisingcontrolling at least the magnitude and/or direction of the appliedstrain.
 9. The method of claim 1, wherein the applied strain isuncontrolled, such that a particular magnitude and/or a particulardirection of the applied strain on at least one of the one or moreoptically readable structures is unpredictable.
 10. The method of claim1, wherein the one or more optically readable structures comprises oneor more continuous or discrete components exhibiting quantum mechanicalconfinement, each component having an intrinsic band structure prior toapplication of the strain, and wherein the applied strain changes theintrinsic band structure to change an optical property of the componentlinked to that quantum mechanical confinement, wherein the confinementof the one or more continuous or discrete components confines in one ormore of 3D, 2D, or 1D, or 0D.
 11. The method of claim 1, wherein the oneor more optically readable structures comprises a 2D material, orconfines in 2D, or comprises 0D quantum dots or confines in 0D, and thestrain is axially applied to the body.
 12. The method of claim 1,wherein the interaction is such that the strain is maintained, after theelement has been made, without an external influence in the form of atleast one of an externally applied temperature change; or an externallyapplied force.
 13. A system for making an optically readable element,the system comprising: a dispenser for providing one or more opticallyreadable structures at least in or on a body, a strain being applied tothe one or more optically readable structures as a result of aninteraction between the body and the one or more optically readablestructures; the one or more optically readable structures each having anintrinsic band structure prior to application of the strain, and whereinthe applied strain changes the intrinsic band structure; and wherein theinteraction is such that the strain is maintained independently ofexternal influences, after the element has been made.
 14. The system ofclaim 13, further comprising an optical reader for optically reading theone or more optically readable structures of the optically readableelement.
 15. An optically readable element comprising: one or moreoptically readable structures at least in or on a body, a strain beingapplied to the one or more optically readable structures as a result ofan interaction between the body and the one or more optically readablestructures; the one or more optically readable structures each having anintrinsic band structure prior to application of the strain, and whereinthe applied strain changes the intrinsic band structure; and wherein theinteraction is such the strain is maintained independently of externalinfluences, after the element has been made.
 16. The optically readableelement of claim 15, wherein the interaction is based on a change instate of the body from a first state to a second state.
 17. Theoptically readable element of claim 15, further comprising a second bodycovering at least a part of the body having the one or more opticallyreadable structures.
 18. The optically readable element of claim 15,wherein one or both of the body and the second body are structured toprovide at least one of: optical filtering with respect to opticalreading of the one or more optically readable structures; protection forthe one or more optically readable structures; stabilisation of anoptical property of the one or more optically readable structures; orcontrol of an average strain at an interface between the body and thesecond body.
 19. The optically readable element of claim 15, wherein theone or more optically readable structures comprises one or morecontinuous or discrete components exhibiting quantum mechanicalconfinement, the or each component having an intrinsic band structureprior to application of the strain, and wherein the applied strainchanges that intrinsic band structure, in order to change an opticalproperty of the component linked to that quantum mechanical confinement,wherein the confinement of the one or more continuous or discretecomponents optionally confines in one or more of 3D, 2D, or 1D, or 0D.20. The optically readable element of claim 15, wherein the one or moreoptically readable structures comprises a 2D material, or confines in2D, or comprises 0D quantum dots or confines in 0D, and the strain isaxially applied to the body.